1. Field of the Invention
The present invention relates to an apparatus for increasing an operation speed of a boom on excavators, which enables an operator to increase a lifting speed of the boom and simultaneously decrease a rotation speed of an upper swing structure when the boom is operated in a vertical plane (lifting) simultaneously with rotation of the upper swing structure in a horizontal plane (swing).
More particularly, the present invention relates to an apparatus for increasing an operation speed of a boom on excavators, which enables an unskilled operator to conveniently manipulate a working device by decreasing a rotation speed of the swing and increasing a lifting speed of the boom relatively when the excavator performs combined operation containing the lifting of the boom and the swing of the upper swing structure to improve its working efficiency.
2. Description of the Prior Art
A conventional excavator includes, as shown in FIG. 1, a lower driving structure 1; an upper swing structure 5 mounted on the lower driving structure 1 and rotated in a horizontal plane by a driving means having a swing motor 2, a pinion gear 3 fixed on the swing motor 2, and an internal gear 4 meshed with the pinion gear 3; a operation cab 6 and an engine 7 mounted on the upper swing structure 5; a working device 14 mounted on the upper swing structure 5 and having a boom 9 driven by a boom cylinder 8, an arm 11 driven by an arm cylinder 10, and a bucket 13 driven by a bucket cylinder 12; and a counterweight 15 mounted on the rear side of the upper swing structure 5 and having a weight (not shown) so as to maintain a balance of the equipment at working.
Referring to FIG. 2, a power generating unit driving the excavator includes an engine 16, a hydraulic pump 17 driven by the engine 16 to supply a hydraulic fluid to an actuator(s) A; 8, 10, and 12 of the working device 14, and a control valve 18 installed in a flow path between the hydraulic pump 17 and the actuator 17 to control the hydraulic fluid supplied to the actuator A.
Reference numeral “19” denotes a radiator, “20” denotes an oil cooler cooling the hydraulic fluid to be returned, and “21” denotes a hydraulic tank.
A conventional hydraulic circuit for driving the boom and the swing motor includes, as shown in FIG. 3, first and second hydraulic pumps 16a and 16b connected to the engine 16; a first actuator 8 (i.e., a boom cylinder) connected to the first hydraulic pump 16a; and a second actuator 2 (i.e., a swing motor) connected to the second hydraulic pump 16b. 
The conventional hydraulic circuit for driving the boom and the swing motor also includes a first control valve 22 installed in flow paths 25 and 26 between the first hydraulic pump 16a and the first actuator 8 and switched to control startup, stop, and turnabout of the first actuator 8; a second control valve 23 installed in flow paths 29 and 30 between the second hydraulic pump 16b and the second actuator 2 and switched to control startup, stop, and turnabout of the second actuator 2; and a third control valve 24 installed in flow paths 27 and 28 between the second hydraulic pump 16b and the first actuator 8 (in this case, the flow paths 27 and 28 are communicated with the flow paths 25 and 26 connected to the first control valve) and switched to join a part of the hydraulic fluid of the second hydraulic pump 16b into the first actuator 8.
The operation of lifting the boom will now be described with reference to FIG. 3.
If a control signal is inputted to the right port of the first control valve 22 by an operator, an inner spool of the first control valve 22 is shifted in a left direction on the figure (i.e., it is shifted to the position a). The hydraulic fluid discharged from the first hydraulic pump 16a is supplied to a large chamber of the first actuator 8 via the first control valve 22 and the flow path 25 to lift the boom 9. At that time, the hydraulic fluid discharged from the first actuator 8 is returned to the hydraulic tank via the flow path 26 and the first control valve 22.
By contrast, if the first control valve 22 is shifted in a right direction on the figure (i.e., to the position b), the hydraulic fluid discharged from the first hydraulic pump 16a is supplied to a small chamber of the first actuator 8 via the first control valve 22 and the flow path 26 to lower the boom 9. In this case, the hydraulic fluid discharged from the first actuator 8 is returned to the hydraulic tank via the flow path 25 and the first control valve 22.
The operation of swinging the upper swing structure will now be described with reference to FIG. 3.
If a control signal is inputted to the left port of the second control valve 23 by the operator, an inner spool of the second control valve 23 is shifted in a right direction on the figure (i.e., it is shifted to the position e). The hydraulic fluid discharged from the second hydraulic pump 16b is supplied to the second actuator 2 via the second control valve 23 and the flow path 30 to rotate the swing motor 2.
Thus, the pinion gear 3 fixed to the swing motor 2 is meshed with the internal gear 4 fixed to the upper swing structure 5 to rotate the upper swing structure 5. At that time, the hydraulic fluid discharged from the second actuator 2 is returned to the hydraulic tank via the flow path 29 and the second control valve 23.
The principle of increasing the lifting speed of the boom will now be described with reference to FIG. 3.
When the operator operates the control lever to lift the boom, a control signal is inputted to the left port of the third control valve 24 by the operator, and thus an inner spool of the third control valve 24 is shifted to the left direction on the figure (i.e., it is shifted to the position c). The hydraulic fluid discharged from the second hydraulic pump 16b is supplied to the first actuator 8 via the third control valve 24 and the flow paths 27 and 25. That is, a part or all of the hydraulic fluid discharged from the second hydraulic pump 16b is joined into the first actuator 8 to increase the lifting speed of the boom 9.
The hydraulic fluid discharged from the first actuator 8 is returned to the hydraulic tank via the flow path 26 and the first control valve 22, and simultaneously, the hydraulic fluid is returned to the hydraulic tank via the flow path 28 and the third control valve 24. At this time, the first control valve 22 is opened, and then the third control valve 24 is opened.
The operation of lifting the boom simultaneously with the rotation of the upper swing structure will be now described with reference to FIG. 3.
At the excavation and loading work on to a dump truck, the bucket 13 is pressed into the soil ground by the combined operation work of boom down, arm in, and bucket in motion, and then lifted up by boom up operation. After that, the upper swing structure 5 is swung to load the soil onto the dump truck. The above process is repeatedly carried. In this case, the operator conducts the operation of lifting the boom 9 and swinging the upper swing structure 5 at the same time, in order to cut down a cycle time.
In this case, since a load is given to the bucket 13 with the soil loaded therein, the lifting speed of the boom 9 becomes slower, while the rotation speed of the upper swing structure 5 becomes relatively faster due to the increased pressure. Thus, while the operator waits during the lifting time of the boom 9, the operator has to decrease the rotation speed of the upper swing structure 5 by adjusting lever stroke for swing speed control. Therefore, in the case of manipulating lifting the boom simultaneously with the rotation of the upper swing structure to perform the combined operation, experience and skill are required to the operator.